Image forming apparatus, image forming method and non-transitory computer-readable storage medium

Abstract

An image forming apparatus includes an image forming device forming an image, a fixing device for heat-fixing the image on a sheet, a belt for conveying the sheet toward the fixing device, a sensor, and a control device configured to control the image forming device to form marks bridging over the belt and the sheet having passed through the fixing device at both ends of the sheet, obtain a length between remaining marks left on the belt after the sheet having the marks formed thereon is conveyed to a downstream side of the belt, on the basis of an output signal of a sensor which output is changed depending on whether there are the marks, and adjust a printing magnification of an image to be formed on the sheet on the basis of the length between the remaining marks.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 an image forming device configured to form an image; 
 a fixing device configured to heat-fix the image on a sheet; 
 a belt configured to convey the sheet toward the fixing device; 
 a sensor; and 
 a control device configured to:
 control the image forming device to form marks bridging over the belt and the sheet having passed through the fixing device at a first end of the sheet and at a second end of the sheet that is opposite to the first end; and 
 adjust a printing magnification of an image to be formed on the sheet, comprising:
 obtaining a length between remaining marks left on the belt after the sheet having the marks formed thereon is conveyed to a downstream side of the belt, on the basis of an output signal of the sensor of which an output is changed depending on whether there are the marks formed on the sheet; and 
 adjusting the printing magnification of the image to be formed on the sheet on the basis of the length between the remaining marks. 
 
 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein in the adjusting the printing magnification, the control device is configured to individually adjust the printing magnification on a first surface of the sheet, which is first printed upon a duplex printing, and on a second surface of the sheet, which is later printed. 
     
     
       3. The image forming apparatus according to  claim 1 , wherein in the adjusting the printing magnification, the control device is configured to:
 obtain a deviation value from a reference position of the remaining marks on the basis of the output signal of the sensor; and 
 adjust the printing magnification on the basis of the deviation value and the length between the remaining marks. 
 
     
     
       4. The image forming apparatus according to  claim 1 , wherein in the adjusting the printing magnification, the control device is configured to adjust, based on the length between the remaining marks in a first direction, the printing magnification in a second direction. 
     
     
       5. The image forming apparatus according to  claim 1 , wherein the control device is configured to control the image forming device to form the marks in a case of printing internal data on the sheet. 
     
     
       6. The image forming apparatus according to  claim 1 , wherein in the adjusting the printing magnification, the control device is configured to change a printing magnification, which is to be obtained on the basis of a next output signal of the sensor, on the basis of a printing magnification obtained when a mark for manual adjustment is printed on the sheet and a printing magnification obtained on the basis of the output signal of the sensor. 
     
     
       7. The image forming apparatus according to  claim 1 , wherein the control device is configured to control the image forming unit to form the marks in response to detecting at least one of a change in the number of sheets except for a printing, an increase in a sheet feeding tray, a replacement of the sheet and an opening or closing operation of the sheet feeding tray. 
     
     
       8. The image forming apparatus according to  claim 1 ,
 wherein a plurality of the image forming devices is provided, and 
 wherein in the controlling the image forming device to form the marks, the control device is configured to form the marks by using the same image forming device. 
 
     
     
       9. The image forming apparatus according to  claim 1 ,
 wherein in the controlling the image forming device to form the marks, the control device is configured to control the image forming device to form the marks even though the sheet, which is a formation target of the marks, does not pass through the fixing device, and 
 wherein in the adjusting the printing magnification, the control device is configured to adjust the printing magnification of the image, based on a length between remaining marks of the marks formed at a state where the sheet does not pass through the fixing device, and the length between the remaining marks of the marks formed after the sheet passed through the fixing device. 
 
     
     
       10. The image forming apparatus according to  claim 1 ,
 wherein the control device is configured to obtain a length of the sheet, and 
 wherein in the adjusting the printing magnification, the control device is configured to adjust the printing magnification of the image based on the length of the sheet obtained in the obtaining the length of the sheet and the length between the remaining marks obtained by the output signal of the sensor. 
 
     
     
       11. The image forming apparatus according to  claim 1 , further comprising:
 a re-conveyance mechanism configured to convey the sheet having passed through the fixing device toward an upstream side of the belt, 
 wherein the sheet on which the marks are formed in the formation processing is a sheet having passed through the fixing device having been returned to the belt by the re-conveyance mechanism and having been conveyed by the belt. 
 
     
     
       12. The image forming apparatus according to  claim 1 , wherein the control device is configured to:
 control the image forming device to form first marks bridging over the belt and a first side of the sheet before passing through the fixing device at both ends of the sheet; 
 after the sheet having the first marks formed thereon is conveyed to a downstream side of the belt, obtain a first interval between remaining first marks left on the belt and a first length between the remaining first marks; 
 convey the sheet having passed through the fixing device toward an upstream side of the belt by using a re-conveyance mechanism; 
 control the image forming device to form second marks bridging over the belt and a second side of the sheet having passed through the fixing device at both ends of the sheet; 
 after the sheet having the first marks formed thereon is conveyed to the downstream side of the belt, obtain a first interval between remaining second marks left on the belt and a second length between the remaining second marks; 
 obtain a sheet shrinkage ratio on the basis of the first interval and the second interval; 
 obtain a positional deviation ratio on the basis of the first length and the second length; and 
 adjust the printing magnification on the basis of at least one of the sheet shrinkage ratio and the positional deviation ratio. 
 
     
     
       13. The image forming apparatus according to  claim 12 , wherein the control device is further configured to:
 in the controlling the image forming device to form the first marks, control the image forming device to form a mark for manual adjustment on the sheet; 
 receive a measured value on the basis of the mark for manual adjustment; 
 obtain a sheet shrinkage ratio on the basis of the received measured value; 
 obtain a correction coefficient on the basis of the sheet shrinkage ratio on the basis of the received measured value and the sheet shrinkage ratio on the basis of the first interval and the second interval; and 
 change a printing magnification, which is to be obtained on the basis of a next output signal of the sensor, with using the correction coefficient. 
 
     
     
       14. The image forming apparatus according to  claim 1 , wherein the control device is configured to:
 obtain a size of the sheet; 
 convey the sheet to pass through the fixing device and toward an upstream side of the belt by using a re-conveyance mechanism; 
 control the image forming device to form the marks bridging over the belt and the sheet having passed through the fixing device at the first end of the sheet and the second end of the sheet; 
 after the sheet having the marks formed thereon is conveyed to the downstream side of the belt, obtain an interval between remaining marks left on the belt a length between the remaining second marks; 
 obtain a sheet shrinkage ratio on the basis of the size of the sheet and the interval between the remaining marks; 
 obtain a positional deviation ratio on the basis of the length between the remaining second marks; and 
 adjust the printing magnification on the basis of at least one of the sheet shrinkage ratio and the positional deviation ratio. 
 
     
     
       15. An image forming method of an image forming apparatus comprising an image forming device configured to form an image, a fixing device configured to heat-fix the image on a sheet, and a belt configured to convey the sheet toward the fixing device, the image forming method comprising:
 controlling the image forming device to form marks bridging over the belt and the sheet having passed through the fixing device at a end of the sheet and at a second end of the sheet that is opposite to the first end; and 
 adjusting a printing magnification of an image to be formed on the sheet, comprising:
 obtaining a length between remaining marks left on the belt after the sheet having the marks formed thereon is conveyed to a downstream side of the belt, on the basis of an output signal of a sensor of which an output is changed depending on whether there are the marks formed on the sheet; and 
 adjusting the printing magnification of the image to be formed on the sheet on the basis of the length between the remaining marks. 
 
 
     
     
       16. The image forming method according to  claim 15 , wherein in the adjusting the printing magnification, the method comprises individually adjusting the printing magnification on a first surface of the sheet, which is first printed upon a duplex printing, and on a second surface of the sheet, which is later printed. 
     
     
       17. The image forming method according to  claim 15 , wherein in the adjusting the printing magnification, the method comprises:
 obtaining a deviation value from a reference position of the remaining marks on the basis of the output signal of the sensor; and 
 adjusting the printing magnification on the basis of the deviation value and the length between the remaining marks. 
 
     
     
       18. A non-transitory computer-readable storage medium having a computer program stored thereon and readable by a computer of an image forming apparatus, the image forming apparatus comprising an image forming device configured to form an image; a fixing device configured to heat-fix the image on a sheet; a belt configured to convey the sheet toward the fixing device and a sensor, the computer program, when executed by the computer, causes the image forming apparatus to perform operations comprising:
 controlling the image forming device to form marks bridging over the belt and the sheet having passed through the fixing device at a first end of the sheet and at a second end of the sheet that is opposite to the first end; and 
 adjusting a printing magnification of an image to be formed on the sheet, comprising:
 obtaining a length between remaining marks left on the belt after the sheet having the marks formed thereon is conveyed to a downstream side of the belt, on the basis of an output signal of the sensor of which an output is changed depending on whether there are the marks formed on the sheet; and 
 adjusting the printing magnification of the image to be formed on the sheet on the basis of the length between the remaining marks. 
 
 
     
     
       19. The non-transitory computer-readable storage medium according to  claim 18 , wherein in the operation of adjusting the printing magnification, the computer program causes the computer to perform an operation of individually adjusting the printing magnification on a first surface of the sheet, which is first printed upon a duplex printing, and on a second surface of the sheet, which is later printed. 
     
     
       20. The non-transitory computer-readable storage medium according to  claim 18 , wherein in the operation of adjusting the printing magnification, the computer program causes the computer to perform operations comprising:
 obtaining a deviation value from a reference position of the remaining marks on the basis of the output signal of the sensor; and 
 adjusting the printing magnification on the basis of the deviation value and the length between the remaining marks.